An extensive laboratory reaction kinetics study was performed on the "direct process" of methyl chloride and silicon, also commonly referred to as the methylchlorosilane (MCS) reaction. Temperature and concentrations of copper, zinc, and tin were varied. Reaction rate reproducibility and repeatability were improved by increasing temperature homogeneity in our fixed-bed reactor system. A stripped gas chromatograph (GC) oven, a detailed standard operating procedure, and small-diameter fixed-bed reactors were used to achieve good temperature control. The kinetics study incorporated multiple sample points per run as opposed to a single sample. The complete kinetics data set was analyzed with statistical analysis tools (SAS, Minitab). Three silicon utilization windows (0-15%, 15-30%, and g30%) were assumed to determine reaction rate descriptions by so-called transfer functions. The developed model supports a proposal wherein at least two processes exist. The main reaction (the MCS reaction) produces dimethyldichlorosilane (Di) and equimolar amounts of trimethylchlorosilane (mono) and methyltrichlorosilane (Tri). At least one side reaction occurs during the MCS deactivation phase resulting in higher levels of Tri and other byproducts.

GE Silicones ran a commercial direct process production unit with low aluminum content silicon, and very poor reaction yields were obtained. The direct process is used to react silicon with methyl chloride to produce methylchlorosilanes, which are used to produce silicone materials. Laboratory experiments were conducted that allowed GE to generate a plausible hypothesis to explain the commercial failure. The commercial and laboratory results have been used by GE to diagnose additional direct process reaction problems. Aluminum is an important impurity found in chemical-grade silicon. Aluminum acts as one of many promoters in the direct process. Laboratory experiments indicated that the presence of aluminum is required to increase the vapor pressure of the zinc promoter at direct process reaction conditions. Increased vapor pressure allows movement of zinc within the solid reaction mass present in the fluid-bed reactor. Insufficient zinc vapor pressure causes severe problems with raw material yields and product quality that translates to uneconomic operation of the commercial direct process reaction unit.